Scott and Hill.—Strlecture of Isoetes Hystrix. 437 
is scarcely developed in our short-spined form. All these 
spinous structures are firmly seated on the sclerotic belt below. 
The inner tissue of the leaf-base remains living, and, when 
the lamina is thrown off, is covered in by a transverse plate 
of hard black tissue. 
The whole structure is called by Braun the phyllopodium, 
a term which has since been used by Bower in a much more 
extended sense. In the reduced sterile leaves almost the 
whole organ is used up to form the persistent scale. The 
appearance of the ordinary spinose leaf-base is shown in 
Fig. 28. 
The Roots. 
As regards the apex of the root we have nothing to add 
to the results of previous observers. In this case there can 
be no question that the earlier writers (Hofmeister, 1853, 
p. 136; Nageli and Leitgeb, 1868, p. 135) were mistaken in 
referring the growth to a single apical cell, while Kienitz 
Gerlofif (1881, p. 793) was equally in error in regarding the 
tissue of the apex as ‘ a completely indifferent meristem/ 
Bruchmann, Farmer, and Campbell have proved conclusively 
that the root-apex possesses distinct histogenetic layers. 
The plerome is perfectly well defined. Bruchmann (1874, 
p. 556) and Farmer (1890, p. 52) find that it grows by means 
of a single initial cell 1 . Some of our sections appear to 
confirm this result in the case of I. Hystrix , but we doubt 
whether it holds good constantly in our species. Beyond the 
plerome the most distinct demarcation is between inner and 
outer cortex (Farmer, 1890, p. 51). 
It appears that the later growth of the root is intercalary, 
so that the apex can only be studied with advantage in quite 
young roots. 
Dichotomy of the roots takes place very early, while the 
apex is still buried in the tissues of the stem. 
The anatomical structure of the mature root of Isoetes is 
1 Compare also Nageli and Leitgeb, 1868, p. 134, * Der Cambiumcylinder ist 
anfangs immer einzellig.’ 
